Fixes #2796: Added BootstrapInterface.

docs/guide/extensions.md

@@ -82,7 +82,7 @@ Yii2 uses Composer for installation, and extensions for Yii2 should as well. Tow
 
 If your extension classes reside directly in the repository root directory, you can use the PSR-4 autoloader in the following way in your `composer.json` file:
 
-```
+```json
 {
     "name": "myname/mywidget",
     "description": "My widget is a cool widget that does everything",
@@ -109,18 +109,55 @@ If your extension classes reside directly in the repository root directory, you
 
 In the above, `myname/mywidget` is the package name that will be registered
 at [Packagist](https://packagist.org). It is common for the package name to match your Github repository name.
-
-In the above, the `psr-4` autoloader is specified, mapping the `myname\mywidget` namespace to the root directory where the classes reside.
+Also, the `psr-4` autoloader is specified in the above, which maps the `myname\mywidget` namespace to the root directory where the classes reside.
 
 More details on this syntax can be found in the [Composer documentation](http://getcomposer.org/doc/04-schema.md#autoload).
 
+
+### Bootstrap with extension
+
+Sometimes, you may want your extension to execute some code during the bootstrap stage of an application.
+For example, your extension may want to respond to the application's `beginRequest` event. You can ask the extension user
+to explicitly attach your event handler in the extension to the application's event. A better way, however, is to
+do all these automatically.
+
+To achieve this goal, you can create a bootstrap class by implementing [[yii\base\BootstrapInterface]].
+
+```php
+namespace myname\mywidget;
+
+use yii\base\BootstrapInterface;
+use yii\base\Application;
+
+class Bootstrap implements BootstrapInterface
+{
+    public function bootstrap(Application $app)
+    {
+        $app->on(Application::EVENT_BEFORE_REQUEST, function () {
+             // do something here
+        });
+    }
+}
+```
+
+You then list this bootstrap class in `composer.json` as follows,
+
+```json
+{
+    "extra": {
+        "bootstrap": "path\\to\\MyBootstrapClass"
+    }
+}
+```
+
+
 Working with database
 ---------------------
 
-Extensions sometimes have to use their own database tables. In such situations, 
+Extensions sometimes have to use their own database tables. In such a situation,
 
 - If the extension creates or modifies the database schema, always use Yii migrations instead of SQL files or custom scripts.
-- Migrations should be applicable to as many data storages as possible.
+- Migrations should be applicable to different database systems.
 - Do not use Active Record models in your migrations.
 
 Assets

framework/CHANGELOG.md

@@ -151,7 +151,7 @@ Yii Framework 2 Change Log
 - Enh #2729: Added `FilterValidator::skipOnArray` so that filters like `trim` will not fail for array inputs (qiangxue)
 - Enh #2735: Added support for `DateTimeInterface` in `Formatter` (ivokund)
 - Enh #2756: Added support for injecting custom `isEmpty` check for all validators (qiangxue)
-- Enh #2775: Added `yii\base\Application::bootstrap` to support running bootstrap classes when starting an application (qiangxue)
+- Enh #2775: Added `yii\base\Application::bootstrap` and `yii\base\BootstrapInterface` to support running bootstrap classes when starting an application (qiangxue)
 - Enh: Added support for using arrays as option values for console commands (qiangxue)
 - Enh: Added `favicon.ico` and `robots.txt` to default application templates (samdark)
 - Enh: Added `Widget::autoIdPrefix` to support prefixing automatically generated widget IDs (qiangxue)

framework/base/Application.php

@@ -133,8 +133,9 @@ abstract class Application extends Module
      */
     public $extensions = [];
     /**
-     * @var array list of bootstrap classes. A bootstrap class must have a public static method named
-     * `bootstrap()`. The method will be called during [[init()]] for every bootstrap class.
+     * @var array list of bootstrap classes or their configurations. A bootstrap class must implement
+     * [[BootstrapInterface]]. The [[BootstrapInterface::bootstrap()]] method of each bootstrap class
+     * will be invoked at the beginning of [[init()]].
      */
     public $bootstrap = [];
     /**
@@ -223,8 +224,9 @@ abstract class Application extends Module
     {
         $this->initExtensions($this->extensions);
         foreach ($this->bootstrap as $class) {
-            /** @var Extension $class */
-            $class::bootstrap();
+            /** @var BootstrapInterface $bootstrap */
+            $bootstrap = Yii::createObject($class);
+            $bootstrap->bootstrap($this);
         }
         parent::init();
     }
@@ -243,9 +245,9 @@ abstract class Application extends Module
                 }
             }
             if (isset($extension['bootstrap'])) {
-                /** @var Extension $class */
-                $class = $extension['bootstrap'];
-                $class::bootstrap();
+                /** @var BootstrapInterface $bootstrap */
+                $bootstrap = Yii::createObject($extension['bootstrap']);
+                $bootstrap->bootstrap($this);
             }
         }
     }

framework/base/BootstrapInterface.php

+<?php
+/**
+ * @link http://www.yiiframework.com/
+ * @copyright Copyright (c) 2008 Yii Software LLC
+ * @license http://www.yiiframework.com/license/
+ */
+
+namespace yii\base;
+
+/**
+ * BootstrapInterface is the interface that should be implemented by classes who want to participate in the application bootstrap process.
+ *
+ * The main method [[bootstrap()]] will be invoked by an application at the beginning of its `init()` method.
+ *
+ * Bootstrap classes can be registered in two approaches.
+ *
+ * The first approach is mainly used by extensions and is managed by the Composer installation process.
+ * You mainly need to list the bootstrap class of your extension in the `composer.json` file like following,
+ *
+ * ```json
+ * {
+ *     // ...
+ *     "extra": {
+ *         "bootstrap": "path\\to\\MyBootstrapClass"
+ *     }
+ * }
+ * ```
+ *
+ * If the extension is installed, the bootstrap information will be saved in [[Application::extensions]].
+ *
+ * The second approach is used by application code which needs to register some code to be run during
+ * the bootstrap process. This is done by configuring the [[Application::bootstrap]] property:
+ *
+ * ```php
+ * return [
+ *     // ...
+ *     'bootstrap' => [
+ *         "path\\to\\MyBootstrapClass1",
+ *         [
+ *             'class' => "path\\to\\MyBootstrapClass2",
+ *             'prop1' => 'value1',
+ *             'prop2' => 'value2',
+ *         ],
+ *     ],
+ * ];
+ * ```
+ *
+ * As you can see, you can register a bootstrap class in terms of either a class name or a configuration class.
+ *
+ * @author Qiang Xue <qiang.xue@gmail.com>
+ * @since 2.0
+ */
+interface BootstrapInterface
+{
+    /**
+     * Bootstrap method to be called during application bootstrap stage.
+     * @param Application $app the application currently running
+     */
+    public function bootstrap(Application $app);
+}

framework/base/Extension.php

-<?php
-/**
- * @link http://www.yiiframework.com/
- * @copyright Copyright (c) 2008 Yii Software LLC
- * @license http://www.yiiframework.com/license/
- */
-
-namespace yii\base;
-
-/**
- * Extension is the base class that may be extended by individual extensions.
- *
- * Extension serves as the bootstrap class for extensions. When an extension
- * is installed via composer, the [[bootstrap()]] method of its Extension class (if any)
- * will be invoked during the application initialization stage.
- *
- * @author Qiang Xue <qiang.xue@gmail.com>
- * @since 2.0
- */
-class Extension
-{
-    /**
-     * Initializes the extension.
-     * This method is invoked at the beginning of [[Application::init()]].
-     */
-    public static function bootstrap()
-    {
-    }
-}